Human Biological Evolution

1. Human Biological Evolution

2. Introduction… • Many different human-like species existed over the 4-8 million years since our lineage split from apes – collectively, we call these species hominids. • Some of these species would have lived at the same time, and not all of them are the direct ancestors of modern humans. • We don’t know the exact progression from species to species that led to modern humans. There are many different ideas, and as new fossils are discovered the gaps become filled and the picture becomes clearer.

3. A.   Pan troglodytes, chimpanzee, modern B.   Australopithecus africanus, STS 5, 2.6 My C.   Australopithecus africanus, STS 71, 2.5 My D.   Homo habilis, KNM-ER 1813, 1.9 My E.   H. habilis, OH24 , 1.8 My F.   H. ergaster (H. erectus), KNM-ER 3733, 1.75 My G.   H. heidelbergensis, "Rhodesia man," 300-125ky H.   Homo neanderthalensis, La Ferrassie 1, 70ky I.    H. neanderthalensis, La Chappelle-aux-Sts, 60ky J.   H. neanderthalensis, Le Moustier, 45ky K.   Homo sapiens, Cro-Magnon I, 30ky L.   Homo sapiens, modern

4. Ardipithecusramidus… • Fossils found in Ethiopia • Sometimes classed as an early Australopithecus. • May represent the earliest stage of homonin evolution. • Many features showing adaptation both to bipedalism and brachiation

5. The Australopithecines were the earliest known pre-humans. All of the various species lived in Africa. Australopithecus = “southern ape man”

6. They mostly lived in the East African Rift Valley and in Southern Africa.

7. They were all bipedal with brains slightly bigger than a chimps, smaller canines and possibly using wooden tools like chimps do. • Their fossils show that bipedalism preceded increased brain size. • Bipedalism freed up the hands. • Australopithecines can be described as either gracile (slender) or robust (heavily built) according to their skull and dental structure. • The robust types were specialist herbivores and an evolutionary side-branch.

8. Australopithecines can be described as either gracile (slender) or robust (heavily built) according to their skull and dental structure. The robust types were specialist herbivores and an evolutionary side-branch.

9. Australopithecus afarensis ‘Lucy’ is the best known example. Had an ape-like face with low forehead, brow ridges, flat nose and no chin. Otherwise human-like. 1-1.5m tall. Brain volume 400-500cc. Gracile.

10. Sexual dimorphism with males taller than females.

12. Australopithecus- an ape who walked on two legs • One of the most important hominid fossils ever discovered is that of “Lucy”. • Lucy was discovered by Donald Johansson in Hadar, Ethiopia, in 1974. As the team examined the fossil that night, the song “Lucy in the sky with diamonds” was playing, so they named the fossil Lucy. • Lucy belongs to the species Australopithecus afarensis, and lived 3.2 million years ago. She stood around 1.1 metres (3.5 feet) tall and she walked upright on two legs, although she probably had a less graceful gait than us, since she walked with her legs bent. • This discovery confirmed that bipedalism evolved very early in our evolutionary history.

15. Laetoli footprints… A few years after Lucy was found, a set of footprints were discovered in hardened ash in Tanzania. These footprints date to 3-4 million years ago and were probably also made by Australopithecines. The creature that made these footprints undoubtedly walked upright further confirming that our ancestors were bipedal several million years ago. More recently discovered fossils dating back 5-6 million years also show signs of being bipedal. The shift to bipedalism was a highly significant event in our history as it freed the hands to use tools.

16. Tooth rows almost parallel. • Finger bones longer than in humans and slightly curved as in apes. • Lived 3-4mya.

17. Australopithecus afarensis • Australopithecus afarensis: lived 3.2 million years ago. Stood around 1.1 metres (3.5 feet) tall and was bipedal but was also arboreal. Herbivorous.Brain volume 400-500cc. Lucy is the best-know specimen (+ Laetoli footprints). Gracile (lighter build)

18. Australopithecus africanus Less ape-like than A. afarensis with a higher forehead, less obvious brow ridges, small canines, larger molars, no diastema and human-like jaw shape. 1.1 – 1.4m tall. Cranial volume 400-500cc. Gracile. The Taung child

19. Australopithecus africanus… Probably some sexual dimorphism but less than A. afarensis. Lived 2.5-3mya. Fossils found in caves in Africa and identified by Raymond Dart in 1924 – first Australopithecine fossils found (nicknamed the Taung child). Controversial because scientists thought large brains evolved before bipedalism.

20. For your notes – GracileAustralopithecines • Australopithecus afarensis: lived 3.2 million years ago. Stood around 1.1 metres (3.5 feet) tall and was bipedal but was also arboreal. Herbivorous.Brain volume 400-500cc. Lucy is the best-know specimen (+ Laetoli footprints). • Austalopithecusafricanus: lived 3-2.3 mya. Bipedal, males 1.4m tall, females 1.2m tall. Larger brain than A.afarensis and more modern tooth and facial shape. Cranial volume 400-500cc. Taung child is best-known speciment.

21. Robust Australopithecines • May also be classified in the genus Paranthropus. • Includes A. robustus and A. boisei. • Both had huge molars and mandibles. A sagittal crest and wide cheek bones suggests large temporal muscles.

22. Robust Australopithecines • Probably fed on tough vegetation as seen by microwear pattern on teeth. • NB a sagittal crest is not evidence of a herbivorous diet – lions and tigers have very large sagittal crests.

23. A. boisei A. robustus

24. For your notes: • A. robustus lived 1.3 - 2 mya, cranial capacity of 450 - 550cc, height 1.1 - 1.3m. Lived in Southern Africa. • A. boisei lived 1.2 – 2.4mya, cranial capacity of 500 – 530cc, height 1.2 – 1.4m. Discovered in Olduvai Gorge in Tanzania.

28. Bipedalism was the most important event in human evolution because it freed up the hands. The large brain was able to take advantage of this opportunity. All primates have an upright posture.

29. The probable selection pressure for bipedalism was environmental change due to climate change. Tectonic changes caused the uplift of the Himalayas and changes in ocean currents leading to a cooler and drier Earth. This may have been the cause of the African forests receding and being replaced by grassland.

30. Advantage of bipedalism • More energy-efficient at walking speed than knuckle walking. Also generates less heat. • Freed up hands for carrying offspring, food and tools.

31. Keeps body cool with less direct surface area exposed to the sun and greater air flow in drier air to increase sweat evaporation. • Gave greater height for easier detection of food and predators. Upright stance may be more intimidating.

32. Homo habilis • Rounded skull still with brow ridges. Some development of Broca’s region suggesting language. • Small jaw, incisors and canines suggesting an omnivorous diet.

34. 1.5 - 2.4mya in eastern Africa • Cranial volume 500 – 650cc. • 1 – 1.3m tall. • Made stone and bone Oldowan tools. • Some evidence of cooperative hunting and scavenging for food.

35. Oldowan tools

38. Scavenging was a way of finding food during times of shortage. Following other scavengers made it easy to find carcasses. Using stone tools made it easy to break open bones for marrow.

39. Homo erectus • 1.8mya to ~300 000ya. • Cranial volume 750 – 1250cc. • No sagittal crest. Prominent brow ridges. • Maybe capable of speech. • 1.3 – 1.7m tall.

40. Homo erectus Homo sapiens

41. Turkana boy Note human-likeness of knees, pelvis ribcage, skull.

42. Used Acheulean tools such as choppers, hand axes and scrapers. May have hunted and trapped animals. • Used fire to cook food. • Found in Africa, Asia and Europe.

43. Acheulean tools Note how they are worked all over with many small chips removed

44. Homo erectus range

45. H. erectus learned how to use and control fire.

46. Fire was useful for preserving food, making it taste better and killing parasites. Also useful as a deterrent against predators, enabled activity at night and reinforced social bonding.

47. Homo neanderthalensis • 1.5 – 1.7m tall. • Sloping forehead with an occipital bun for attachment of strong neck muscles.

48. Receding chin. Brow ridges present.

49. Cranial volume 1200 – 1750cc (larger than modern humans).

50. Thicker limb bones, stocky build probably a cold adaptation. Large areas for muscle attachment. • Seemed to care for their elderly and disabled.